The bactericidal activity of an aqueous solution of hypochlorous acid varies with the pH of the solution because the state of chlorine compounds dissolved in the aqueous solution varies with pH.
When the pH of an aqueous solution of hypochlorous acid is 8 or more, or the aqueous solution of hypochlorous acid is alkaline, hypochlorous acid ions (ClO.sup.-) having fairly low bactericidal activity are mainly present in the aqueous solution. Thus, the bactericidal activity of an alkaline aqueous solution of hypochlorous acid is fairly low.
When the pH of aqueous solution of hypochlorous acid is 7 or less, or the aqueous solution of hypochlorous acid is acidic, the amount of hypochlorous acid (HClO) which has bactericidal activity 10 to 100 times larger than that of hypochlorous acid ions, is larger than the amount of hypochlorous acid ions. Thus, the bactericidal activity of an acidic aqueous solution of hypochlorous acid is high.
When the pH of an aqueous solution of hypochlorous acid is 5.5 or less, substantially 100% of the chlorine compound dissolved in the aqueous solution is hypochlorous acid. Thus, the bactericidal activity of the aqueous solution of hypochlorous acid becomes even higher.
When the pH of an aqueous solution of hypochlorous acid is 3 or less, a part of the chlorine compound dissolved in the aqueous solution becomes chlorine gas (Cl.sub.2) having higher bactericidal activity than that of hypochlorous acid. Thus, the bactericidal activity of the aqueous solution of hypochlorous acid becomes even higher.
Acid sterilizing liquid containing hypochlorous acid can instantly kill bacteria such as Escherichia coli, MRSA, Staphylococcus aureus, etc. Acid sterilizing liquid containing hypochlorous acid can cure inflamed parts of the human body suffering from atopy dermatitis, body parts suffering from necrosis owing to diabetes, and bedsores of a bedridden old person. It is thought that acid sterilizing liquid containing hypochlorous acid kills MRSA present on such diseased parts, in this way suppressing itch and suppuration of the parts and thereby curing them.
The skin is damaged by application of acid sterilizing liquid containing hypochlorous acid at a high concentration.
There is a need for an apparatus for generating and dispensing strong acid sterilizing liquid which contains hypochlorous acid at a concentration of about 2 ppm, the concentration prescribed by Japanese City Water Organization in its water purifier examination manual, whose pH is 3 or less, and which is suitable for use on the human body.
A continuously generating type apparatus having a barrier type electrolytic cell has been developed for generating acid liquid containing hypochlorous acid. In this apparatus, salt water is passed through a channel formed between a positive electrode plate and a negative electrode plate disposed to face opposite surfaces of a barrier membrane, and DC voltage is applied between the electrodes to electrolyze the salt water.
At the positive electrode, hydroxide ions (OH.sup.-) contained in the salt water give electrons to the positive electrode to become oxygen gas and are eliminated from the water. Thus, the concentration of hydrogen ions (H.sup.+) in the water flowing through the space between the barrier membrane and the positive electrode increases to make the water acidic. Also at the positive electrode, chlorine ions (Cl.sup.-) contained in the salt water give electrons to the positive electrode to become chlorine gas (Cl.sub.2). The chlorine gas dissolves in the acidic water to become hypochlorous acid.
At the negative electrode, hydrogen ions (H.sup.+) contained in the salt water are given electrons from the negative electrode to become hydrogen gas and are eliminated from the water. Also at the negative electrode, sodium ions (Na.sup.+) and hydroxide ions (OH.sup.-) contained in the salt water are bonded together to become sodium hydroxide. Thus, the water flowing through the space between the barrier membrane and the negative electrode becomes alkaline.
The barrier membrane prevents the mixing of the products at the positive electrode and the products at the negative electrode. Acid liquid containing hypochlorous acid can be obtained by taking the water flowing through the space between the barrier membrane and the positive electrode out of the electrolytic cell.
The conventional continuously generating type apparatus for generating acid liquid containing hypochlorous acid having a barrier type electrolytic cell has a number of problems such as the following.
1. The conventional continuously generating type apparatus having a barrier type electrolytic cell cannot generate strong acid sterilizing liquid which contains hypochlorous acid at a concentration of about 2 ppm, whose pH is 3 or less, and which is suitable for use on the human body. The abbreviation "ppm" used here means concentration by weight converted into chlorine atoms and means "Cl mg/liter".
The inventors of the present invention studied why the conventional continuously generating type apparatus having a barrier type electrolytic cell cannot generate strong acid sterilizing liquid which contains hypochlorous acid at a concentration of about 2 ppm, whose pH is 3 or less, and which is suitable for use on the human body. Their conclusion was as follows.
When the pH of the electrolyzed water must be decreased, the electric current applied across the electrodes must be increased to increase the quantity of the electrolyzed salt water, thereby increasing the concentration of hydrogen ions in the electrolyzed water. Electrons are transferred between hydroxide ions, hydrogen ions and the electrodes at the surfaces of the electrodes. When the electric current is increased, the supply of hydroxide ions and hydrogen ions to the surfaces of the electrodes becomes insufficient, which suppresses the increase in the electric current.
When the voltage applied across the electrodes is increased to increase the supply of the hydroxide ions and hydrogen ions to the surfaces of the electrodes, overvoltage at the positive electrode increases and the generation of chlorine gas is promoted. Thus, the layer of the water flow near the positive electrode becomes strong acid liquid containing hypochlorous acid at a high concentration.
One countermeasure for overcoming the problem of the short supply of the hydroxide ions and hydrogen ions to the surfaces of the electrodes is to narrow the distance between the electrodes, thereby increasing the speed of the flow of the salt water through the channel between the electrodes. However, narrowing the distance between the electrodes is difficult because of the presence of the barrier membrane between the electrodes.
As can be seen from the foregoing explanation, a conventional continuously generating type apparatus having a barrier type electrolytic cell cannot generate strong acid sterilizing liquid which contains hypochlorous acid at a concentration of about 2 ppm, whose pH is 3 or less, and which is suitable for use on the human body.
Strong acid sterilizing liquid which is generated only by the electrolysis of salt water, which contains hypochlorous acid at a concentration of about 2 ppm, whose pH is 3 or less, and which is suitable for use on the human body has not been put to practical us, as described above, the conventional continuously generating type apparatus having a barrier type electrolytic cell cannot generate strong acid sterilizing liquid which contains hypochlorous acid at a concentration of about 2 ppm, whose pH is 3 or less, and which is suitable for use on the human body. According to a recent report, moreover, electrolyzed salt water which is diluted with nothing other than water, which contains hypochlorous acid at a concentration of about 2 ppm, and which is strongly acidic has hardly any bactericidal activity. This conclusion is based on tests using strong acid liquid containing hypochlorous acid at a low concentration which is obtained by adding sterilized distilled water to strong acid liquid containing hypochlorous acid at a high concentration generated by electrolysis of salt water, thereby diluting the strong acid liquid (Pharmacology and Clinical Medicine 1993/VOL.3/NO.9/SEP. page 71 table 1). The inventors of the present invention think that the reported lack of bactericidal activity arises because the hypochlorous acid was broken down into chlorine gas when the aqueous solution was diluted and the chlorine gas left the aqueous solution, thus reducing the bactericidal activity of the aqueous solution.
2. A barrier type electrolytic cell is large because of the presence of the barrier membrane between the electrodes. Thus, the conventional continuously generating type apparatus for generating acid liquid containing hypochlorous acid having a barrier type electrolytic cell is large and not portable. Conventionally, acid liquid containing hypochlorous acid generated in a continuously generating type apparatus having a barrier type electrolytic cell has therefore been stored in a tank and poured from the tank into a small vessel or sprayer for use. Hypochlorous acid is easily broken down by ultraviolet light and the chlorine component evaporates with the lapse of time. Thus, the bactericidal activity of the acid liquid containing hypochlorous acid decreases while it is stored in the tank.
3. Inflammation owing to atopy dermatitis often appears at a hidden part of the body. Therefore, it is preferable to provide an apparatus for generating and dispensing acid liquid containing hypochlorous acid which can be used in a bathroom. In a conventional continuously generating type apparatus having a barrier type electrolytic cell, the space between the electrodes is wide, about 4 mm or greater, owing to the presence of the barrier membrane between the electrodes, the electric resistance of the salt water present between the electrodes is large, and a large amount of electric power is needed to electrolyze the salt water. Thus, a conventional continuously generating type apparatus having a barrier type electrolytic cell has to be driven by domestic AC line current. However, AC line current is not ordinarily available in a bathroom. Thus, an apparatus for generating and dispensing acid liquid containing hypochlorous acid based on a conventional continuously generating type apparatus for generating acid liquid containing hypochlorous acid having a barrier type electrolytic cell cannot be used in a bathroom.